High intensity shot peening

ABSTRACT

A high intensity peening flap construction comprising an elongate strap having at least one metal peening particle support base mechanically fastened adjacent one end thereof and a plurality of refractory hard, impact fracture resistant peening particles metallurgically joined to an exposed face of the support base.

United States Patent Winter Sept. 10, 1974 [54] HIGH INTENSITY SHOT PEENING 3,512,311 5/1970 Block 51/334 3,638,464 2/1972 2 Winter 72/53 [75] Inventor P wmter, whlte Bear Lake 3,645,049 2/1972 Huppert 51 /334 3,696,563 10/1972 I Rands 5l/332 [73] Assignee: Minnesota Mining and Mimufacturmg Company Paul Primary Examiner-Charles W. Lanham Assistant Examiner--Gene P. Crosby [22] Filed; July 16, 1973 Attorney, Agent, or Firm-Alexander, Sell, Steldt & 21 Appl. No.: 379,249 Delahum Related US. Application Data [63] Continuation-in-part of Ser. No. 244,510, April 17, [57] ABSTRACT I972, abandoned.

A high intensity peening flap construction comprising [52] US. Cl...' 72/53, 51/334 an elongate strap having at least one metal peening [51] Int. Cl C2ld 7/06 particle support base mechanically fastened adjacent [5 8] Field of Search 72/53; 5l/334, 337, 332, one end thereof and a plurality of refractory hard, im- 51/401, 402 pact fracture resistant peening particles metallurgically joined to an exposed face of the support base. [56] References Cited UNITED STATES PATENTS 17 Claims, 12 Drawing Figures 2,771,720 11/1956 Field 51/337 HIGH INTENSITY SHOT PEENING CROSS-REFERENCE TO RELATED APPLICATION FIELD OF THE INVENTION The present invention relates to a'peening flap construction useful for high intensity peening.

BACKGROUND OF THE INVENTION It has long been customary to shot peen to increase fatigue strength, to relieve tensile stresses that contribute to stress-corrosion cracking, to form and straighten metal parts, to remove heavy scale, etc. The prior art shot peening processes are described in numerous patents including U.S. Pats. Nos. 2,542,955 and 2,982,007. In conventional shot peening, spheroidal particles of cast steel, cast iron, glass, etc. are blown or mechanically impelled in a high velocity stream against the surface to be treated. The individual shot particles produce shallow, rounded overlapping dimples in the surface, stretching it radially from each point of impact and causing cold working in plastic flow. The resultant compressive stress tends to counteract tensile stresses imparted to the substrate by the preceding rolling, bending, abrading, and similar processes.

The degree of peening, which is generally expressed as peening intensity, is a function of the weight, size, hardness and velocity of the peening particles, exposure time, type of substrate, angle of impingement, and various other factors. It is conventional to express peening intensity in terms of Almen arc height, according to SAE Test I442, described in some detail in Military Specification MlL-S-l3l65B. In this test, a thin, flat piece of steel is clamped to a solid block and exposed to a blast of shot, which, as previously indicated tends to stress the surface, so that the strip will be curved when removed from the block. Test strips are SAE 1070 cold rolled spring steel uniformly hardened and tempered to a hardness of 44-50 Rockwell C, 3 i

0.015 inches long and 0.745 0.750 inch wide. The strips are one of three thicknesses: A, 0.05] i 0.01 inch; C, 0.0938 i- 0.001 inch; and N, 0.031 t 0.001 inch. The height of arc of the resultant chord in mils is referred to as the Almen arc height, greater heights indicating greater peening intensities for a given test strip thickness.

Effective though it is for many purposes, conventional shot peening suffers from disadvantages which drastically limit its usefulness. For example, large and expensive equipment is required for rapidly impelling shot toward a surface and collecting, screening and recirculating the shot particles. Equipment of this type is not readily portable, and hence is suitable only for those metal pieces or parts which can be brought to the shot peen station. It is virtually impossible to use equipment of this type to shot peen a part while it still remains attached to another piece of equipment.

The foregoing drawbacks of conventional shot peening are overcome with respect to low intensity shot peening by the device disclosed in U.S. Pat. No. 3,638,464 assigned to the assignee of the present application. The device there disclosed comprises an annufective.

lus of radially extending peripherally separated flaps which are united at the radially inner ends to a rigid core. Each such flap is a flexible, tough, tear-resistant fiber support to which shot peening particles are bonded at spaced portions by a strong, tough organic adhesive. In use, the annulus is mounted on a shaft and rotated rapidly while the periphery is forced against the substrate to be peened. While the device is extremely effective for low intensity peening application it has been found that the fibrous flaps and the adhesive break 'down in high intensity applications. Until now conventional shot peening had to be used where only high intensity shot peening was economical and/or ef- SUMMARY OF THE INVENTION retention. At least one peening particle support base is mechanically fastened to the elongate strap adjacent one end thereof, which support base is formed of a metal having the ability to withstand high bending and impact stresses while resisting deformation. A plurality of refractory hard, impact fracture resistant peening particles are metallurgically joined to an exposed face of the support base. In use, one or more of the flaps are mounted on a hub with the support base and the peening particles thereon at the ends of the flaps away from the hub. The hub is rotated while the flaps are forced against the substrate to be peened. The peening particles on each support base strike the substrate in turn, thereby causing the peening particles to perform their normal peening function, but preventing the normal uncontrolled scattering which occurs in conventional shot peening.

DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a perspective view of a device utilizing a plurality of high-intensity peening flaps constructed in accordance with a first embodiment of the present invention;

FIG. 2 is a front view of one of the flaps illustrated in FIG. 1;

FIG. 3 is an edge view of the flap illustrated in FIG. 2;

FIG. 4 is a rear view of the flap illustrated in FIG. 2;

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 2;

FIG. 6 is a perspective view of a second embodiment of a high-intensity peening flap constructed in accordance with the present invention and mounted on a shaft;

FIG. 7 isa face view of the flap illustrated in FIG. 6;

FIG. 11 is an edge view of the flap illustrated in FIG. and

FIG. 12 is a rear view of the flap illustrated in FIG. 10.

Referring now to FIGS. 1 through 5 there is illustrated a first embodiment of a high-intensity peening flap, generally designated 10, constructed in accordance with the present invention. The flap comprises an elongate strap 12, two peening particle support bases 14 and 15 anda plurality of peening particles 17.

The elongate strap 12 is formed of a flexible, resilient, tough, shock-absorbing, tear-resistant material having a high flexural endurance and shape retention. The strap 12 must have these properties to withstand the peening impact while retaining the peening particle support bases 14 and 15 thereon and to return the peening particles to position for further peening impacts. A highly satisfactory combination of required properties has been found in a polyurethaneimpregnated nylon scrim known as Reevecote 7625 available from Reeves Brothers, Inc. with offices at New York, NY. Neoprene impregnated nylon scrim has also been found very satisfactory. These materials have the required properties with the tensile strength, tear resistance, and shape retention being provided by the nylon scrim.

In the illustrated embodiment the elongate strap 12 is formed by a double length strip of the material folded back upon itself to permit easy attachment to a cylindrical support hub 19. The hub 19 has apertures 20 drilled axially adjacent and communicating with the periphery thereof whereby the folded in the elongate strap 12 is moved radially inward of the hub and a cylindrical pin is then inserted in the fold and axially down the aperture 20 to retain the strap 12 on the hub 19. The peening particle support bases 14 and 15 are firmly affixed to the elongate strap 12 adjacent and equally spaced from the overlapping ends thereof. Each support base is formed of a metal having the ability to withstand high bending and impact stresses while resisting deformation. These properties serve to aid in retaining the peening particles on the support base and in proper position while at the same time absorbing stresses which would damage or destroy the peening particles.

In the illustrated embodiment the peening particle support bases 14 and 15 are mechanically fastened to the elongate strap 12 by being formed as a rivet. The shank of the rivet is passed through an aperture in both layers of the strap 12, a washer 16 is then slipped over the rear of the shank, and the rear of the shank is thereafter flared to securely fasten the support base to the elongate strap. Within the scope of the present invention other methods of mechanically fastening the support base securely to the elongate strap may also be used; for example, the support base may be formed with a threaded shank onto which a nut is threaded.

In the case of the illustrated rivet-type attachment, the material of the peening particle support base 14 or 15 must in addition to the above requirements be sufficiently ductile to allow the required deformation for fastening. Annealed 1008 steel has been found to have a highly satisfactory combination of the required properties.

The peening particles are of a refractory-hard, impact fracture-resistant material and they are metallurgically joined to the exposed face of the support bases 14 and 15. The particle support bases 14 and 15 and the peening particles 17 must, of course, by compatible for metallurgical joining. Such bonding may be accomplished by brazing, casting the peening particles in place in the support base, sintering or any other available method for forming the require bond.

Refractory-hard, impact fracture-resistant peening particles are utilized because the particles must retain their integrity during the life of the peening flap in order to maintain constant impact pressure. Refractory hard cemented tungsten carbide shot have been found to have an excellent combination of the required propertiesHowever, other cemented carbides, for example, TiC and TaC; ceramic materials, for example, B.,C and hot-pressed alumina as well as other wear-resistant, refractory-hard peening particles are also useful.

The elongate strap 12 is slit between the peening particle support bases 14 and 15 perpendicular to its end to permit independent peening action by the particles on the separate support bases 14 and 15.

FIG. 1 illustrates six of the high intensity peening flaps 10 attached to a hub 19 in the manner previously described. The hub 19 has a central shaft which is inserted in the chuck of a drill 22 to provide rotation of the flap wheel. Activation of the drill causes rotation of the hub 19 to cause impacting of the peening particles 17 against a surface 23 which is desired to be peened.

EXAMPLE 1 One specific example of the peening flap 10 illustrated in FIGS. 1 through 5 will now be described. A No. 4 Tinners rivet (annealed 1008 steel) was chosen for the peening particle support bases 14 and 15. The face of the rivet was drilled with a l/16-inch diameter drill to produce nine holes 0.025 inch deep and spaced 0.075 inch apart in a centered square array. The drilled face was then sand blasted and coated with brazing flu and the rivet was placed in a carbon block.

The peening particles 17 chosen were 0.045 inch diameter tungsten carbide shot. The shot was placed in the. holes in the face of the rivet, a disk of silver brazing alloy (50% Ag, 22% Cu, 20% Zn, 7% Cd, 1% Sn) was placed on top of each shot and the top of the carbon block was installed to hold the shot in place. Heating to form the required metallurgical bond was then accomplished in a continuous flow induction furnace at a temperature of 1,325F. at a rate of six molds per minute. The flux was removed by soaking in hot water for 10 minutes. The rivet shanks were thereafter cut to 0.25 inch length and drilled 0.15 inch deep to produce a 0.22 inch wall thickness.

The strips l inch wide and 5 inches long were cut from 0.038 inch thick Reevecote 7625, a nylon scrim reinforced polyurethane sheeting. The long dimension of the strip was in the warp direction of the sheeting. The. material was then folded transversely in half to form the elongate strap and two 3/ 1 6-inch diameter holes were punched through both layers at the end away from the fold. The holes were located one-fourth inch from the long and short sides and separated by one-half inch. A l-inch long cut was made down the middle of the strap between the holes.

The shank of a peening particle support base 14 or 15 with particles 17 thereon was then passed through the hole in the elongate strap 12. A %-inch diameter steel washer 16 with a 0.191 inch drilled intemal diameter was then slipped over the back of the rivet shank resistant woven fiber support to which shot peening particles are bonded at spaced portions by a strong,

tough, organic adhesive. The low intensity wheel had a The flap assemblies were driven with a hand-held air Powered, ysr n Theumtat iafla ass bl e were operated at a maximum flap deflection (i.e. minimum practical mandrel to work piece distance) and weight of a peening particle support base 14 or 15, the 5 moved 4 inches across a 2.25 inches thick 1020 steel particles 17 and the washer 16 was approximately 0.08 test Plate at a rate whleh would Produce 100 Percent ounce. Scale m a Ther u tsargas tql pwsj--. M... Referring now to FIGS. 6 through 8, there is illustrated a high-intensity peening flap generally desig- LIFEJNTENSITY nated 26, representing a second embodiment of the LT S d I present invention. The same material properties are ree Pee memw quired for each of the elements of the peening flap 26 Assembly (Mmutes) (RPM) (Mus C) of this second embodiment as already described with Levi/intensity wheel 30 3000 respect to the peening flap 10 of the first embodiment Peemng Flap 26 and, therefore, the properties and the range of useful 5 materials will not again be described.

The peening fiap 26 comprises an elongate strap 28, SCALE REMOVAL PERFORMANCE two peening particle support bases 30 and 31 which are aided in being retained on the strap 28 by washers 32, of Area} Impacted I and a plurality of peening particles 33 on each Support Assembly gig in /232$) lo c i i il efi val base and 31. The materials and method of joining the peening particles 33 to the support bases 30 and 31 ,5 intensity wheel 15 eemng Flap 26 90 1.1 and of fastening the supportbases 30 and 3l tothe PEENING INTENSITY (mils Almen c I Speed (RPM) Assembly 750 1000 1500 2000 2500 3000 3500 4000 Low Intensity Wheel 2 3 3.5 4 4.5 Peening Flap 26 l0 l4 l7 l9 elongate strap 28 in the illustrated second embodiment The Life-Intensity table shows that the peening flap are exactly as described above with respect to the peen- 26 provides four times the intensity and more than 15 ing flap 10 of the first embodiment. However, in the times the life of the low intensity wheel. The Scale Repeening flap 26 of the second embodiment th eeni moval Performance table demonstrates that the peenparticle support bases 30 and 31 ar fa t d t th ing flap 26 produces six times the removal rate and reelongate strap 28 in opposed relationship at opposite quires y 10 0f the rage Of that Of the low inends of the strap 28. This provides a balanced single tensity wheel for 100 Percent Scale removal- T Lifeflap construction which may be mounted centrally in Scale Removal eapactty of Peehlhg p 26 ethe slotted end of a rod 35 to form a complete peening fore, 35,000 htehes whlle that of the low intensity device wheel is 450 inches", a one hundred fold capacityincrease being obtained with the flap constructed accord- EXAMPLE 2 ing to the present invention. The Peening Intensity o ifi example f a peening fl 26, com table graphically illustrates that the intensity with peenstructed in accordance with the second embodiment as "t flap 26 of the P 9 e illustrated in FIGS. 6 through 8 will now be described. hlgher h th e tam d wtthihe'l tt ttene y. Wh el- Two Smps l/z'inch wlfie l/z'mches long were cut Referring now to FIGS. 9 through 12, there is illusf the Same 0038 mch thlck Reevecote 7625 mate trated a third embodiment of a high-intensity peening used Example The sttlps were Placed flap, generally designated 40, constructed in accorgether t0 define theelehgate Strap 28. dance with the present invention. The same material- The Peehlhg Particle pp bases 30 and 31, the properties are required for each of the elements of the Peehihg particle5 33 and the method of bonding to the elements of the peening flap 40 of this third embodipp bases were the Same as described in Example ment as described with respect to the peening flap 10 1. Further, the support bases 30 and 31 were fastened f th fi t b di to the elongate strap one-fourth inch from the end and Th peening fl 40 comprises an l t t a 42, one-fourth inch from the edges of the strap 28 in the two peening particle support bases 43 and 45 which are same manner as described in Example 1. aided in being retained on the strap 42 by washers 46, When mounted as illustrated in FIG. 6 the'flap 26 and a plurality of peening particles 48 on each support forms a balanced two-flap shot peening wheel. The spebase. The materials and method of joining the peening cific construction of Example 2 was used in a heavy particles 48 to the support bases 43 and 45 and of fasscale removal comparison test against a low-intensity tening the support bases 43 and 45 to the elongate strap shot peening wheel consisting of two flaps bonded to a 42 in the illustrated third embodiment are exactly as core; each flap comprising a flexible, tough, teardescribed above with respect to the peening flap 10 of the first embodiment. However, in this embodiment a rivet 50 positioned centrally of the width of the strap at the base of the slit between the support bases 43 and 45 secures the two portions of the double length strip surface 53 being peened. This reduces wear on the strap material immediately around the support'bases 43 and 45 significantly extending the life of the flap 40 and permitting a greater number of flaps to be used on a hub of given diameter;

Significant improvement in the peening life of the flap 40 is obtained when the peening faces of the support bases 43 and 45 are inclined to the length of the strap 42 at an acute angle of from 25 to 80. As can be seen in FIG. 9, mounting of the flaps 40 on a hub 51 in the manner described for the flap 10 of the first embodiment causes the peening faces of the support bases to be inclined to the radius of the resulting flap wheel through the same acute angle as they are inclined to the length of the strap 42. The optimum angle of inclination, 0, is a function of the hub radius, r, the effective flap length, f, from the hub 51 to the peening particle support bases 43 and 45 and the distance, 0, the hub is off-set from the working surface 53 in use. The relationship is expressed in the following manner:

However, the angle of inclination may be set in a preferred range of from 40 to 70 and perform nearly as effectively in most practical applications.

In one specific example peening flaps 40 constructed with an effective flap length of 1.875 inches and a support base inclination of 45: were used on a 1.5 inch diameter hub 51. It was found that this flap construction had a peening life approximately four times that of a similar flap having the peening faces of the support bases parallel to the length of the strap. In addition this inclination allowed the use of twelve flaps on the hub on which only three of the straight flaps could be used. Further development work on this flap construction revealed that the optimum angle of inclination of the support bases was 65 i 5 which increased the flap life to five times that of similar straight flaps 10.

I claim: l. A high-intensity peening flap construction com-' prising:

an elongate strap of a flexible, resilient, tough, shockabsorbing, tear-resistant material having a high flexural endurance and shape retention,

at least one peening particle support base mechanically fastened to said elongate strap adjacent one end thereof, said support base being formed of a metal having the ability to withstand high bending and impact stresses while resisting deformation, and

a plurality of refractory hard, impact fractureresistant peening particles metallurgically joined to an exposed face of said support base.

2. The peening flap construction of claim I wherein two particle support bases are mechanically fastened to said elongate strap adjacent one end thereof, said support bases being equally spaced from said one end of said strap and similarly affixed thereon and said strap being slit perpendicular to said one end between said support bases to permit independent peening action by said peening particles on the respective support bases.

3. The peening flap construction of claim 1 wherein at least one particle support base is mechanically fastened to said elongate strap adjacent each end thereof.

4. The peening flap construction of claim 1 wherein said elongate strap is formed of a fiber reinforced polymeric material.

5. The peening flap construction of claim 1 wherein said peening particles comprise a cemented carbide.

6. The peening flap construction of claim 1 wherein said particle support base comprises a rivet, the shank thereof extending through an aperture in said elongate strap and being riveted to the strap.

7. The peening flap construction of claim 6 wherein said particle support base comprises an annealed steel.

8.The peening flap construction of claim 1 wherein said peening particle support base is fastened to said elongated strap at an acute angle of inclination of the peening face thereof to the length of said strap of from 25 to 80.

9. The peening flap construction of claim 8 wherein said acute angle of inclination is from 40 to 10. A high-intensity peening flap construction comprising:

an elongate strap of a flexible, resilient, tough, shockabsorbing, tear-resistant material having a high flexural endurance and shape retention,

at least one peening particle support base mechanically fastened to said elongate strap adjacent one end thereof and at an acute angle of inclination of the peening face of said support base to the length of said strap of from 25 to said support base being formed of a metal having the ability to withstand high bending and impact stresses while resisting deformation, and

a plurality of refractory hard, impact fractureresistant peening particles metallurgically joined to an exposed face of said support base.

11. The peening flap construction of claim 10 wherein said acute angle of inclination is from 40 to 70.

12. The peening flap construction of claim 10 wherein two particle support bases are mechanically fastened to said elongate strap adjacent one end thereof, said support bases being equally spaced from said one end of said strap and similarly affixed thereon and said strap being slit perpendicular to said one end between said support bases to permit independent peening action by said peening particles on the respective support bases.

13. The peening flap construction of claim 10 wherein at least one particle support base is mechanically fastened to said elongate strap adjacent each end thereof.

14. The peening flap construction of claim 10 wherein said elongate strap is formed of a fiber reinforced polymeric material.

9' 15. The .peening flap construction of claim 10 elongate strap and being riveted to the strap. wherein said peening particles comprise a cemented 7 The peening fl construction f claim 16 carbide.

16. The peening flap construction of claim 10 wherein said particle support base comprises a rivet, '5 nealed SteeL the shank thereof extending through an aperture in said wherein said particle support base comprises anan- UNITED STATES OFFICE CERTIFICATE OF CORRECTION I Patent No. 183L200 I Dated Sept. 10,197

Inventofls) PHILLIP M. WINTER It is certified that error appears in the aboveidentified patent and that said Letters Patent ,are hereby corrected as shown beloy:

In the Specification:

Col. 3, line 33 "folded" shouldabe -fold;

.Col. line 7, "require" should be -required--;

Col. 6, line 52-53, "of th'e elements" (second occurrence) should be deleted; 'i

Col. 7, lines 5-9 insert -As an alternative construction,

end of an elongate strap similar to the embodiment of Figures 6 through 8 with the peening faces of the Support'bases inclined to the length of the strap.--; In the Claims: v

Col. 8, line 26, "elongated" should be -elong;ate-.

(Claim 8) Signed and sealed this 17th day of December 1974.

one particle support base may be fastened adjacent each (SEAL) Attest: v McCOY M. GIBSON JR. c. MARSPALL DANN Arresting Officer Commissioner of Patents FQRM P-15 (1M9) v V v v uscomA-oo GOSll-PI i U. VIII-ll "will. OIIICI 2 "I. D MM 

1. A high-intensity peening flap construction comprising: an elongate strap of a flexible, resilient, tough, shockabsorbing, tear-resistant material having a high flexural endurance and shape retention, at least one peening particle support base mechanically fastened to said elongate strap adjacent one end thereof, said support base being formed of a metal having the ability to withstand high bending and impact stresses while resisting deformation, and a plurality of refractory hard, impact fracture-resistant peening particles metallurgically joined to an exposed face of said support base.
 2. The peening flap construction of claim 1 wherein two particle support bases are mechanically fastened to said elongate strap adjacent one end thereof, said support bases being equally spaced from said one end of said strap and similarly affixed thereon and said strap being slit perpendicular to said one end between said support bases to permit indepEndent peening action by said peening particles on the respective support bases.
 3. The peening flap construction of claim 1 wherein at least one particle support base is mechanically fastened to said elongate strap adjacent each end thereof.
 4. The peening flap construction of claim 1 wherein said elongate strap is formed of a fiber reinforced polymeric material.
 5. The peening flap construction of claim 1 wherein said peening particles comprise a cemented carbide.
 6. The peening flap construction of claim 1 wherein said particle support base comprises a rivet, the shank thereof extending through an aperture in said elongate strap and being riveted to the strap.
 7. The peening flap construction of claim 6 wherein said particle support base comprises an annealed steel.
 8. The peening flap construction of claim 1 wherein said peening particle support base is fastened to said elongated strap at an acute angle of inclination of the peening face thereof to the length of said strap of from 25* to 80*.
 9. The peening flap construction of claim 8 wherein said acute angle of inclination is from 40* to 70*.
 10. A high-intensity peening flap construction comprising: an elongate strap of a flexible, resilient, tough, shock-absorbing, tear-resistant material having a high flexural endurance and shape retention, at least one peening particle support base mechanically fastened to said elongate strap adjacent one end thereof and at an acute angle of inclination of the peening face of said support base to the length of said strap of from 25* to 80*, said support base being formed of a metal having the ability to withstand high bending and impact stresses while resisting deformation, and a plurality of refractory hard, impact fracture-resistant peening particles metallurgically joined to an exposed face of said support base.
 11. The peening flap construction of claim 10 wherein said acute angle of inclination is from 40* to 70*.
 12. The peening flap construction of claim 10 wherein two particle support bases are mechanically fastened to said elongate strap adjacent one end thereof, said support bases being equally spaced from said one end of said strap and similarly affixed thereon and said strap being slit perpendicular to said one end between said support bases to permit independent peening action by said peening particles on the respective support bases.
 13. The peening flap construction of claim 10 wherein at least one particle support base is mechanically fastened to said elongate strap adjacent each end thereof.
 14. The peening flap construction of claim 10 wherein said elongate strap is formed of a fiber reinforced polymeric material.
 15. The peening flap construction of claim 10 wherein said peening particles comprise a cemented carbide.
 16. The peening flap construction of claim 10 wherein said particle support base comprises a rivet, the shank thereof extending through an aperture in said elongate strap and being riveted to the strap.
 17. The peening flap construction of claim 16 wherein said particle support base comprises an annealed steel. 